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EBL and AC Issue

Old 03-13-2019, 08:17 PM
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EBL and AC Issue

Hey guys. It's me again. Need a bit of assistance with another item.

I've gotten the idle down great. In gear, park to drive, fan on and just idling in the driveway out of gear are all tame. However, I've got one last issue I'm trying to wrap my head around. It's with the Air Conditioning. When the AC is switched on with the car idling OUT of gear, everything goes wonky. Now, I'm including a datalog and I know that the fueling between cells is playing a role here, but I think there may be a tad more going on.

What I've noted so far is that when the AC is commanded on with the transmission IN GEAR, the reaction is not perfect but it's very decent. It's switching the AC on OUT of gear that poses the biggest issue. Immediately when the AC is commanded on, there is a considerable 300ish RPM sag, immediately followed by the RPM shooting back up, then it eventually settles for a bit and then begins a back and forth process of settling then surging.

Like I said, IN GEAR it comes on much better however, one anomaly I've noticed is the IAC counts. With the transmission IN gear, the initial IAC counts are around 70-80ish. Then when the AC is commanded on, there is a very slight sag in RPM but it quickly equalizes. However, I can then watch the IAC counts max themselves out. At first, it hit the IAC count limit of 160. I went into the tune and increased the maximum IAC steps to 200. It took a bit longer to reach, but even that setting eventually maxed the IAC steps out. Another thing I've noticed is that after turning the AC back off, the idle will hang high around 1600RPM for 20ish seconds while the IAC settles back down IF the transmission was IN gear. So AC in gear, super high IAC counts. AC out of gear, IAC counts are acceptable but everything goes haywire.

I've attached a datalog of the AC being turned on OUT of gear where most of the sagging and surging occurs. I also included an "In gear" log for S&Gs/reference. Anyone see anything out of the normal?

For reference, here are my AC settings in the tune. I've tried tweaking them up and down. When I zero out the Idle increase with AC on, the sag gets worse, the surging gets worse and it's overall a bigger crapshow. If I increase the additional steps and bump steps with AC on, there is still an initial RPM sag but the resulting RPM spike from catching itself is much higher.

IAC - Additional Steps With AC: 15
IAC - Init Steps With No AC: 22 (This is the one parameter I have not played around with)
IAC - AC On Bump Steps: 10
IAC - Idle Increase AC On: 50

What is going on here!?
Attached Files
File Type: zip
AC ON.zip (175.1 KB, 2 views)

Last edited by FireDemonSiC; 03-14-2019 at 11:46 AM.
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Old 03-14-2019, 08:19 PM
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Re: EBL and AC Issue

Alright. Let me post an update.

DISREGARD previously posted logs in terms of surging. I did a few more logs, made some revisions to the low speed VE table so there wasn't as drastic of a change between offending cells and the surging has been eliminated. OUT OF GEAR, when the AC is turned on, there is still the initial sag but then it quickly grabs itself, shoots back up in RPM slightly and then immediately equalizes. Given the fact that the compressor clutch is turning on along with activating the fan at the same time, I don't think there's any way around this even with the solid state timer that places a 10 second delay before turning on the second fan.

However, I am trying to figure out the last issue which is AC on IN GEAR. When the AC is commanded on with the transmission in gear, the transition is smoother. There is no RPM sag and there is only the tiniest hiccup in RPM. However, the problem still remains with the IAC counts. They shoot way up, max out, and then if the AC is turned back off, all is well until you put the transmission back into neutral.

The RPMs still shoot up to around 1500 and hang there for 20-30 seconds while the IAC adjusts itself back down and eventually settles back down to normal idle speed.

Why is it doing this?
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Old 03-15-2019, 08:02 AM
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Re: EBL and AC Issue

Because the IAC is open so far it takes a while for it to close. Should be able to add to this parameter to help reduce it:

IAC - AC On Bump Steps:

I did look at the logs and with the in gear log I didn't see the IAC max out. It did go up though.

The out of gear log showed the IAC at 39 - 40 at idle. Should open the throttle blades to get that in the 20 - 25 step range.

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Old 03-15-2019, 09:41 AM
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Re: EBL and AC Issue

Just throwing this out there -- are you sure the IAC is good -- programming against a sluggish IAC will cause you issues? Have you hooked up manifold gauges to the AC to make sure you pressures are right? If you have too much pressure or moisture in the system the AC compressor can take a lot of power to run it. I've seen it drag to the point the belt starts to slip even.
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Old 03-15-2019, 01:55 PM
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Re: EBL and AC Issue

Originally Posted by RBob View Post
Because the IAC is open so far it takes a while for it to close. Should be able to add to this parameter to help reduce it:

IAC - AC On Bump Steps:

I did look at the logs and with the in gear log I didn't see the IAC max out. It did go up though.

The out of gear log showed the IAC at 39 - 40 at idle. Should open the throttle blades to get that in the 20 - 25 step range.

RBob.
Bob,

Fornicated with the throttle stop screw some. Needs an additional turn but I got the IAC steps down to 30 - 35 at idle out of gear. Here is a new log. This time I turned the AC on and let it do its thing. You will see where it steadily creeps up the counts until they max out at 200. Before I turn the log off I then switch the AC off and place the transmission in neutral where you can see the idle hang high for a good bit until it settles back down.

Why does it take so long for the IAC to react? Is this normal behavior? Also, would you recommend any other changes besides the bump step setting? Should I increase the maximum IAC steps Scalar even more?

Originally Posted by Aviator857
Just throwing this out there -- are you sure the IAC is good -- programming against a sluggish IAC will cause you issues? Have you hooked up manifold gauges to the AC to make sure you pressures are right? If you have too much pressure or moisture in the system the AC compressor can take a lot of power to run it. I've seen it drag to the point the belt starts to slip even.
The IAC is about 8 years old. I bought it as a NOS ACDelco back in 2011. I've put roughly 35k miles on it. Also, AC is working is working just fine.
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AC IN GEAR.zip (217.9 KB, 3 views)
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Old 03-16-2019, 11:30 AM
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Re: EBL and AC Issue

Why are you running the engine so lean while at idle?

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Old 03-16-2019, 12:10 PM
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Re: EBL and AC Issue

Originally Posted by RBob View Post
Why are you running the engine so lean while at idle?

RBob.
I tried their advice in this thread and it actually worked. You couldn't really even hear the cam at idle until I leaned the fuel out.

Thoughts?




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Old 03-17-2019, 09:01 AM
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Re: EBL and AC Issue

Likely went too lean. I looked at your other thread and the cam you are running isn't that radical.

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Old 03-17-2019, 01:53 PM
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Re: EBL and AC Issue

Originally Posted by RBob View Post
Likely went too lean. I looked at your other thread and the cam you are running isn't that radical.

RBob.

I too was skeptical at first. However, it's just what it likes. I've had it as lean as 22:1 on the wideband and it still wasn't surging yet. Right now I have it set to 18:1. I tried it in the neighborhood of 15-16 but you could hear the overlap really start to disappear around that AFR. Also, plugs indicate that it's happy.

FWIW I also fixed the AC issues I started this thread for. I took your advice and increased bump steps from 10 to 30. Also bumped VE slightly around those cells and increased maximum IAC to 220, as well as got the IAC counts down to the correct 20-25 reading at idle. It doesn't hang high anymore coming out of gear and there is no more surging at all. The only thing that remains is that slight sag when AC is commanded on which I'll live with.
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